Miotic agents are frequently used by ophthalmologic surgeons during intraocular surgery. The anterior chamber is irrigated with a miotic agent after delivery of the lens in cataract surgery as well as in penetrating keratoplasty, iridectomy and other anterior segment surgery. Prompt miosis is necessary to ensure that a round pupil is obtained after cataract surgery. If any of the iris of the eye is caught in the incision or if a capsular tag is caught in the incision, the pupil will be distorted on the following day. It is easy to miss a capsular tag in the incision since the tag is clear and transparent unless one uses a miotic agent. The other advantages obtained by the use of miotics are the facilitation of post-placed corneal scleral sutures, anterior chamber lens insertion and a decrease in post-operative peripheral anterior synechias. Many surgeons feel that miotic agents help in centering and positioning the intraocular lens implant.
Elevated intraocular pressure (IOP) can interfere with normal functioning and may result in irreversible loss of visual function. Viscoelastic agents such as Healon are often used during lens implantation which can cause elevated IOP with pressure spiking.
With the advent of modern surgical techniques and the trend to "in the bag" placement of posterior chamber intraocular lens' (IOL), more and more viscoelastic substances are being used. Increasingly, cataract surgery is being done on an out-patient basis, and the patient returns to the physician's office the following day. Slit lamps and applanation tonometry are handy, and consequently most surgeons are examining their post-operative patients even better than when they were hospitalized. This has improved patient care and, on the other hand, has perhaps resulted in increased awareness of the IOP 20-24 hours after cataract surgery.
Pressure studies have shown that the IOP in the first 24 hours after cataract surgery may be very important. Damage by raising IOP is possible to the optic nerve, the vascular supply within the eye, and the corneal endothelium (15)(7). Consequently, every effort should be made to control the IOP from the very onset of the post-operative period.
Acetylcholine (Miochol) is the most popular miotic agent utilized by ophthalmologic surgeons. Miochol provides quick miosis (within minutes). However, it provides very poor control of IOP after several hours, even when pressure control agents such as acetazolamide (Diamox) are utilized. Carbachol (Miostat) does not provide as quick a miosis and is not as widely used. A miotic agent providing quick miosis with control of intraocular pressure 24 hours after surgery is needed.